1. Field of the Invention
The present invention relates to an automatic focus detection apparatus and a control method for the same, and more particularly to an automatic focus detection apparatus that performs focus detection using subject detection results and a control method for the same.
The present invention also relates to an image pickup apparatus to which such an automatic focus detection apparatus and a control method for the same are applied.
2. Description of the Related Art
In the autofocus (AF) control of video cameras and the like, a TV-AF system that detects an in-focus position based on the sharpness (contrast) of image signals generated using an image sensor is widely used. The TV-AF system, specifically, is a system that generates AF evaluation values indicating the degree of contrast with regard to image signals captured at different focusing lens positions, and searches for a position of the focusing lens at which contrast is maximized based on the AF evaluation values as the in-focus position.
Also, automatically detecting a region (subject region) having a specific pattern such as a person's face, for example, from an image, and performing exposure and focus detection on the basis of the detected subject region is known. The specific pattern is not limited to a person's face. For example, an image processing apparatus and method that detect an upper half of a person's body are proposed in Japanese Patent Laid-Open No. 2009-211311.
On the other hand, in order to speed up the focus-detecting operation, a method has been proposed in which search driving of the focusing lens is performed before image capture and the position of a subject that should be in-focus is specified from the AF evaluation values acquired in a plurality of focusing areas (AF frames), and then a focusing operation is performed utilizing this position at the time of image capture (Japanese Patent Laid-Open No. 2010-191084).
In the case where a human body detection method described in Japanese Patent Laid-Open No. 2009-211311 or the like is utilized, detection can be performed even if a person has his or her back turned or with a subject that has accessories or the like on his or her face. However, detection error is higher than with face detection, and the AF frame could possibly be set to an unintended subject.
On the other hand, in the case where the subject that should be in-focus differs before and after image capture, the method described in Japanese Patent Laid-Open No. 2010-191084 does not enable the focus-detecting operation to be sped up. Also, there is a problem in that the focusing lens is also driven to positions away from the in-focus position when search driving is performed during image capture in the case of moving image capture, resulting in blurred images being recorded.